Isolation of downhole environments depends on the deployment of a downhole tool that effectively seals the entirety of the borehole or a portion thereof, for example, an annulus between a casing wall and production tube. Swellable packers are particularly useful in that they are capable of generating a contact force against a nearby structure when exposed to one or more downhole fluids such as water, oil, or a combination thereof. Compared with mechanically setup packers and inflatable packers, fluid-swellable packers are easier to set up.
Oil swellable packers normally contain an elastomer such as EPDM that expands when exposed to hydrocarbon based fluids. EPDM rubber often swells rapidly in the oil or oil based fluids and can seal a borehole within one or two days at elevated temperatures. However, under certain circumstances, it is desirable to delay the swelling of the packers to allow the operator to have more time to carry out various completion operations. Such delayed swelling period can be a few days or weeks.
One possible solution is to dispose an outer layer on an EPDM elastomer core to regulate the amount of well fluids that can reach the elastomer core thus controlling the swelling rate of the core. While such proposed packers may have a delayed swelling rate, the outer layer can prevent the core from reaching its full expansion potential and adversely affect the formation of an effective seal. Thus, alternative sealing elements having controlled swelling are desired in the art.